Diagnostic device for secondary battery and recovery method for secondary battery

ABSTRACT

A diagnostic device for a secondary battery having a structure in which positive electrodes and negative electrodes are alternately arranged includes an electronic control unit. The electronic control unit is configured to acquire a first resistance value indicating a magnitude of electrical resistance of the secondary battery, compress at least a part of the secondary battery, acquire a second resistance value indicating a magnitude of electrical resistance of the secondary battery after the compression, determine, using the first and second resistance values, whether an amount of decrease in electrical resistance of the secondary battery by the compression is greater than a predetermined value, and determine whether an increase in resistance due to distortion of at least one of the positive electrodes and the negative electrodes occurs in the secondary battery using a result of the determination.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2020-005875 filed on Jan. 17, 2020, incorporated herein by reference inits entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a diagnostic device and a recoverymethod for a secondary battery.

2. Description of Related Art

Japanese Patent No. 5765258 (JP 5765258 B) discloses a technology inwhich a capacity (hereinafter, also referred to as a “battery capacity”)of a secondary battery having a multilayer electrode structure isacquired, and a constraint force on the secondary battery is adjustedaccording to a degree of a decrease in the battery capacity. Thetechnology is focused on the fact that when a positive electrode activematerial layer of a positive electrode plate of a lithium-ion secondarybattery is cracked, the degree of a decrease in the battery capacity isgreater than before the crack occurs. JP 5765258 B discloses that, whensuch a crack occurs, by compressing the lithium-ion secondary batterymore tightly than before the crack occurs, a gap between the crackportions becomes smaller and the battery capacity is slightly increased.The multilayer electrode structure is a structure in which positiveelectrodes and negative electrodes are alternately arranged, andincludes both a wound body and a multilayer flat plate.

SUMMARY

In the technology described in JP 5765258 B, deterioration of theperformance of the secondary battery is not detected until the activematerial layer is cracked. Once the active material layer is cracked, itis difficult to recover it. In addition, when the battery capacity isdecreased due to another factor, it is not increased even if theconstraint force on the secondary battery is increased.

The present disclosure provides a technology that accurately determineswhether deterioration of recoverable performance of a secondary battery,more specifically, an increase in resistance of the secondary batteryhaving a multilayer electrode structure due to distortion of anelectrode, occurs, and executes a recovery process on the secondarybattery, as needed.

A first aspect of the present disclosure is a diagnostic device for asecondary battery having a structure in which positive electrodes andnegative electrodes are alternately arranged. The diagnostic deviceincludes an electronic control unit. The electronic control unit isconfigured to acquire a first resistance value indicating a magnitude ofelectrical resistance of the secondary battery before compression andcompress at least a part of the secondary battery. The electroniccontrol unit is configured to acquire a second resistance valueindicating a magnitude of electrical resistance of the secondary batteryafter the compression. The electronic control unit is configured todetermine, using the first resistance value and the second resistancevalue, whether an amount of decrease in electrical resistance of thesecondary battery by the compression is greater than a predeterminedvalue. The electronic control unit is configured to determine whether anincrease in electrical resistance due to distortion of at least one ofthe positive electrodes and the negative electrodes occurs in thesecondary battery using a result of the determination on the amount ofdecrease in electrical resistance.

In the secondary battery having a multilayer electrode structure (thatis, a structure in which positive electrodes and negative electrodes arealternately arranged), a gap may be created between the layers when anelectrode composing the multilayer structure is distorted (for example,bent). In the secondary battery having the multilayer electrodestructure, such a gap may act so as to increase a distance between theelectrodes or decrease a contact point (or a contact area) of anelectrode active material. Accordingly, when the distance between theelectrodes is increased or the contact point (or the contact area) ofthe electrode active material is decreased, electrical resistance of thesecondary battery tends to be increased due to a contact failure.

The increase in resistance of the secondary battery due to suchdistortion of the electrode is temporarily resolved by compressing thesecondary battery. In other words, the electrode becomes close to itsoriginal form due to the compression. As distortion of the electrode isdecreased, electrical resistance of the secondary battery is decreased.

In the diagnostic device for the secondary battery, an informationacquisition unit compresses at least the part of the secondary batteryand a first determination unit determines whether the amount of decreasein electrical resistance of the secondary battery by the compression isgreater than the predetermined value. The information acquisition unitmay compress the entire secondary battery, or may selectively compressonly a part where distortion easily occurs or only a part where contactresistance due to distortion is easily increased. As such, when theincrease in resistance of the secondary battery due to distortion of theelectrode occurs, electrical resistance of the secondary battery isdecreased by compressing the distorted part. Therefore, it is possibleto accurately determine whether the increase in resistance due todistortion of the electrode occurs in the secondary battery, using theresult of the determination by the first determination unit.

The secondary battery to be diagnosed may be a single battery, a moduleincluding a plurality of single batteries, or an assembled batterycomposed of the plurality of single batteries (cells) that iselectrically connected to one another.

In the diagnostic device, upon determining that the increase inelectrical resistance due to distortion of at least one of the positiveelectrodes and the negative electrodes occurs in the secondary battery,the electronic control unit may be configured to execute a predeterminedrecovery process. The predetermined recovery process may includecharging, while a load that compresses the secondary battery is appliedto the secondary battery, the secondary battery in a discharged state inwhich a state-of-charge (SOC) of the secondary battery has become equalto or less than a predetermined SOC value.

In the diagnostic device, when the electrode composing the multilayerstructure is distorted, distortion of the electrode is easily resolvedby executing the predetermined recovery process. When the electrodeshifts from a low energy state (that is, a low SOC) to a high energystate (that is, a high SOC), the electrode receives a compression forceapplied by the load and easily returns to its original form. Inaddition, as a voltage is applied between the electrodes and a currentflows, a state of interface between the electrodes is easily stabilized.

The state-of-charge (SOC) indicates a remaining power storage amount.For example, a ratio of a current power storage amount to a powerstorage amount of a fully charged state is represented by 0% to 100%. Asa SOC measuring method, a well-known method, such as a currentintegration method or an open circuit voltage (OCV) estimation method,can be adopted.

The compression force in the predetermined recovery process may bestronger than the compression force applied by the informationacquisition unit. As the compression force in the predetermined recoveryprocess is increased, the electrode tends to return to its original formmore easily. On the other hand, since the compression by the informationacquisition unit is executed when it is not clear whether distortion ofthe electrode occurs, it is desirable that the compression force shouldbe weaker than the compression force in the predetermined recoveryprocess such that a normal electrode (that is, an electrode in whichdistortion does not occur) is not damaged.

The load in the predetermined recovery process may be fixed or variable.As the load is increased, distortion of the electrode is resolved moreeasily. Then, as distortion of the electrode is resolved, electricalresistance of the secondary battery is decreased. However, when the loadexceeds a limit value (hereinafter, also referred to as a “saturationload”), electrical resistance of the secondary battery is not decreasedeven if the load is increased. The load in the predetermined recoveryprocess may be a saturation load which is obtained in advance byexperiments or simulation.

In the diagnostic device, the predetermined recovery process may includerepeating, while the load that compresses the secondary battery isapplied to the secondary battery, discharging the secondary battery suchthat the SOC of the secondary battery becomes equal to or less than thepredetermined SOC value and charging the secondary battery in thedischarged state in which the SOC of the secondary battery has becomeequal to or less than the predetermined SOC value, until electricalresistance of the secondary battery becomes equal to or less than apredetermined value.

As such, by repeating the discharging and the charging, electricalresistance of the secondary battery is sufficiently and easilydecreased.

In the diagnostic device, the electronic control unit may be configuredto compress the secondary battery by applying a load from the outside ofthe secondary battery.

With the above configuration, the secondary battery can be appropriatelycompressed and the compression force can be adjusted according to themagnitude of the load.

In the diagnostic device, the electronic control unit may be configuredto compress the positive electrodes of the secondary battery byexpanding the negative electrodes of the secondary battery.

The negative electrodes and the positive electrodes may have differentdistortion susceptibility depending on the secondary battery. Forexample, when a secondary battery in which negative electrodes that areexpanded during the charging and contracted during the discharging isadopted is used (that is, the charging and the discharging arerepeated), distortion (more specifically, deformation causing a gapbetween the electrodes) of a positive electrode easily occurs. With thediagnostic device, it is possible to easily determine whether anincrease in resistance due to distortion of the positive electrodeoccurs in the secondary battery. In the diagnostic device, theinformation acquisition unit can compress the positive electrodes byexpanding the negative electrodes, and a second determination unit candetermine whether the increase in resistance due to distortion of thepositive electrode occurs in the secondary battery.

A second aspect of the present disclosure is a recovery method for asecondary battery having a structure in which positive electrodes andnegative electrodes are laminated. The recovery method includes a firstcompression for compressing at least a part of the secondary battery, asecond compression for compressing the secondary battery by applying aload from the outside of the secondary battery when an amount ofdecrease in electrical resistance of the secondary battery by the firstcompression is greater than a predetermined value, and a recovery forcharging the secondary battery in a discharged state in which a SOC ofthe secondary battery has become equal to or less than a predeterminedSOC value while the secondary battery is compressed by the secondcompression.

With the recovery method, when distortion of an electrode composing amultilayer structure occurs, the recovery process is executed, such thatdistortion of the electrode is easily resolved.

Each of the first compression and the second compression may be executedby a user or by electronic control.

The secondary battery may be a lithium-ion secondary battery. Thenegative electrodes of the secondary battery may be carbon-basedelectrodes or silicon-based electrodes.

In the lithium-ion secondary battery in which the carbon-basedelectrodes or the silicon-based electrodes are adopted as the negativeelectrodes, the negative electrodes are easily expanded by increasingthe SOC. With the above method, by expanding the negative electrodes,the positive electrodes can be compressed during the charging of thesecondary battery. As such, in the recovery, distortion of the positiveelectrode is easily resolved.

In the recovery method, in the first compression, the positiveelectrodes may be compressed by increasing the SOC of the secondarybattery until the negative electrodes are expanded.

With the above method, in the first compression, the positive electrodescan be easily compressed. Then, whether distortion occurs in thepositive electrodes can be determined based on a change in resistance ofthe secondary battery while the positive electrodes are compressed.

The secondary battery may include a wound electrode body that includesthe positive electrodes and the negative electrodes. The positiveelectrodes and the negative electrodes may be wound around a windingcore while being alternately arranged with separators interposedtherebetween. A longitudinal direction of the winding core may beperpendicular to a winding axis of the wound electrode body. The windingcore may contain an elastic material and may be configured to extend inthe longitudinal direction by a pressing force received from the woundelectrode body.

In the secondary battery, the winding core extends in the longitudinaldirection by the load applied from the outside, and the entireelectrodes (more specifically, the wound electrode body wound around thewinding core) are easily compressed. Therefore, distortion of theelectrode is easily resolved by the load. With the above method, byresolving distortion of the electrode in the secondary battery, theincrease in resistance due to distortion of the electrode is easilyrestricted.

The secondary battery may be a battery collected from an electricallydriven vehicle. The electrically driven vehicle is configured to travelby using power stored in the battery. Examples of the electricallydriven vehicle include a fuel cell (FC) vehicle and a range extendervehicle (EV) in addition to an electric vehicle (EV), a hybrid vehicle(HV), and a plug-in hybrid vehicle (PHV).

With each aspect of the present disclosure, it is possible to accuratelydetermine whether deterioration of recoverable performance of asecondary battery (more specifically, an increase in resistance of thesecondary battery having a multilayer electrode structure due todistortion of an electrode) occurs, and execute a recovery process onthe secondary battery, as needed.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like signs denote likeelements, and wherein:

FIG. 1 is a diagram illustrating a schematic configuration of asecondary battery diagnosed by a diagnostic device for the secondarybattery according to an embodiment of the present disclosure;

FIG. 2 is a diagram illustrating a cross-sectional view of II-II in FIG.1;

FIG. 3 is a diagram for describing a multilayer electrode structure of awound electrode body illustrated in FIG. 2;

FIG. 4 is a diagram illustrating a configuration of the diagnosticdevice for the secondary battery according to the embodiment of thepresent disclosure;

FIG. 5 is a diagram illustrating shapes and arrangements of constraintmembers illustrated in FIG. 4;

FIG. 6 is a diagram illustrating an example of a state of the secondarybattery while compressed by the constraint members illustrated in FIG.5;

FIG. 7 is a diagram for describing a recovery process executed by asecond determination unit illustrated in FIG. 4;

FIG. 8 is a flowchart illustrating a procedure of a diagnosis processexecuted by the diagnostic device for the secondary battery illustratedin FIG. 4;

FIG. 9 is a flowchart illustrating details of a first diagnosis process(including the recovery process) illustrated in FIG. 8;

FIG. 10 is a flowchart illustrating a modified example of the firstdiagnosis process illustrated in FIG. 9; and

FIG. 11 is a diagram illustrating an example of an assembled batterythat is manufactured using a plurality of secondary batteries diagnosedby the diagnostic device for the secondary battery according to theembodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described in detail withreference to drawings. In the drawings, the like or corresponding partsare denoted by the like reference signs, and description thereof willnot be repeated.

FIG. 1 is a diagram illustrating a schematic configuration of asecondary battery diagnosed by a diagnostic device for a secondarybattery according to the present embodiment. With reference to FIG. 1, asecondary battery (hereinafter, simply referred to as a “battery”) 100includes a case 10, a positive electrode terminal 51, and a negativeelectrode terminal 52. In the present embodiment, the battery 100 is aliquid lithium-ion secondary battery that can be mounted on anelectrically driven vehicle (for example, an EV, an HV, or a PHV).Moreover, the case 10 is a rectangular case formed of metal (forexample, aluminum alloy). The case 10 may be provided with a gasdischarge valve (not shown).

FIG. 2 is a diagram illustrating a cross-sectional view of II-II inFIG. 1. With reference to FIG. 2, the case 10 accommodates a woundelectrode body 20 and an electrolytic solution (not shown) that composethe lithium-ion secondary battery. The wound electrode body 20 isaccommodated in the case 10 while being wound around a winding core 40.The winding core 40 has a flat shape. The cross section of the windingcore 40 illustrated in FIG. 2 corresponds to a cross section of thewinding core 40 that is perpendicular to a winding axis C of the woundelectrode body 20. The winding core 40 has an elongated shape, and alongitudinal direction thereof is perpendicular to the winding axis C.The winding core 40 contains an elastic material and is configured toextend in the longitudinal direction by a pressing force received fromthe wound electrode body 20. As the elastic material, a rubber materialcan be adopted. In the present embodiment, as the elastic materialforming the winding core 40, styrene-butadiene rubber is adopted.

FIG. 3 is a diagram for describing a multilayer electrode structure ofthe wound electrode body 20. FIG. 3 illustrates the wound electrode body20 before it is wound around the winding core 40. With reference to FIG.3 together with FIGS. 1 and 2, the wound electrode body 20 is formed ina flat shape by winding strip-shaped electrode sheets around the windingcore 40. More specifically, the wound electrode body 20 illustrated inFIG. 2 is formed by alternately laminating positive electrode sheets 21and negative electrode sheets 22 with separators 23 interposedtherebetween in the order of the positive electrode sheet 21, theseparator 23, the negative electrode sheet 22, the separator 23, . . . ,and then winding the laminated body obtained in the above manner aroundthe winding core 40. The number of electrode sheets can be arbitrary.

In the wound electrode body 20, the positive electrode sheet 21 and thenegative electrode sheet 22 function as a positive electrode and anegative electrode of the battery 100, respectively. In the presentembodiment, positive electrodes and negative electrodes of the battery100 are wound around the winding core 40 while being alternatelyarranged with the separators 23 interposed therebetween so as to formthe wound electrode body 20. The battery 100 includes the woundelectrode body 20 having a multilayer electrode structure (that is, astructure in which positive electrodes and negative electrodes arealternately arranged). In the wound electrode body 20, the separator 23is interposed between the positive electrode sheet 21 and the negativeelectrode sheet 22. The separator 23 may be fixed at the end portion inthe winding direction.

The positive electrode sheet 21 includes a positive electrode currentcollector 21 a and a positive electrode active material layer 21 b. Thepositive electrode active material layer 21 b is formed on both surfacesof the positive electrode current collector 21 a by coating, forexample, a positive electrode mixture including a positive electrodeactive material on the surfaces of the positive electrode currentcollector 21 a (for example, aluminum foil). An example of the positiveelectrode active material includes lithium transition metal oxides. Inthe present embodiment, as the positive electrode active material, aternary positive electrode material of nickel-cobalt-manganese (NCM) isadopted. In other words, the positive electrodes of the battery 100according to the present embodiment are ternary positive electrodes. Thepositive electrode active material layer 21 b may include a conductivematerial (for example, acetylene black) and/or a binder (for example,polyvinylidene fluoride) in addition to the positive electrode activematerial.

The negative electrode sheet 22 includes a negative electrode currentcollector 22 a and a negative electrode active material layer 22 b. Thenegative electrode active material layer 22 b is formed on both surfacesof the negative electrode current collector 22 a by coating, forexample, a negative electrode mixture including a negative electrodeactive material on the surfaces of the negative electrode currentcollector 22 a (for example, copper foil). In the present embodiment, asthe negative electrode active material, a carbon-based material (forexample, graphite) is adopted. In other words, the negative electrodesof the battery 100 according to the present embodiment are carbon-basedelectrodes. The negative electrode active material layer 22 b mayinclude a thickener (for example, carboxymethyl cellulose) and/or abinder (for example, styrene-butadiene rubber) in addition to thenegative electrode active material.

An example of the separator 23 includes a microporous film. Themicropores in the separator 23 facilitate the retention of theelectrolytic solution in the micropores. An example of a material of theseparator 23 includes polyolefin resin, such as polyethylene (PE) orpolypropylene (PP).

The above-described wound electrode body 20 is sealed in the case 10together with the electrolytic solution. Then, the positive electrodecurrent collector 21 a is electrically connected to the positiveelectrode terminal 51 illustrated in FIG. 1, and the negative electrodecurrent collector 22 a is electrically connected to the negativeelectrode terminal 52 illustrated in FIG. 1. The electrolytic solutionmay include an aprotic solvent and a lithium salt (for example, LiPF₆)dissolved in the solvent. Examples of the aprotic solvent includeethylene carbonate (EC), ethylmethyl carbonate (EMC), dimethyl carbonate(DMC), and diethyl carbonate (DEC). Two or more types of solvents may bemixed and used.

FIG. 4 is a diagram illustrating a configuration of the diagnosticdevice for the secondary battery according to the present embodiment.With reference to FIG. 4, a diagnostic device 1 includes an electroniccontrol unit 300, a charger/discharger 400, and a power source 500, andis configured to diagnose the above-described battery 100 (see FIGS. 1to 3). A tag TG that stores information on the battery 100 is attachedto the battery 100. The tag TG stores information indicatingcharacteristics (for example, initial electrical resistance andcapacity) of an initial state of the battery 100. The tag TG may alsostore information on a composition (for example, a material) of thebattery 100. As the tag TG, for example, a radio frequencyidentification (RFID) tag can be adopted. The electronic control unit300 is configured to read and rewrite the information stored in the tagTG by wireless or wired communication.

The battery 100 is further provided with a monitoring unit 110 thatmonitors a state of the battery 100. The monitoring unit 110 includesvarious sensors that detect the state (for example, the temperature,current, and voltage) of the battery 100 and outputs the detectionresult to the electronic control unit 300. The electronic control unit300 can acquire the state (for example, the temperature, current,voltage, state-of-charge (SOC), and electrical resistance) of thebattery 100 based on outputs (detection values of the various sensors)from the monitoring unit 110.

The battery 100 is electrically connected to the charger/discharger 400.The charger/discharger 400 is configured to charge and discharge thebattery 100 according to an instruction from the electronic control unit300. The charger/discharger 400 charges the battery 100 with powersupplied from the power source 500. The charger/discharger 400 mayconvert power discharged from the battery 100 into heat using anelectrical resistor (not shown), or may store the power in apredetermined power storage device (not shown).

The battery 100 is provided with constraint members 31, 32. FIG. 5 is adiagram illustrating shapes and arrangements of the constraint members31, 32. With reference to FIG. 5, the constraint members 31, 32 haveelongated shapes and are arranged parallel to the winding axis C (seeFIG. 2) of the wound electrode body 20. In the present embodiment, theconstraint members 31, 32 are formed of a resin material (for example,polypropylene). The constraint members 31, 32 are arranged so as to faceeach other, with the battery 100 interposed therebetween. The constraintmembers 31, 32 are fixed on surfaces of the case 10 and restrict thecase 10 from being deformed outward. However, the constraint members 31,32 may be fixed by an arbitrary method, and the constraint members 31,32 may be supported by an arm (not shown). Alternatively, the constraintmember 31 and the constraint member 32 may be fastened to each other.

Returning to FIG. 4, the diagnostic device 1 further includes anactuator 200 that activates the constraint members 31, 32. The actuator200 presses the constraint members 31, 32 against the battery 100 byactivating the constraint members 31, 32, thereby applying a load to thebattery 100. The battery 100 interposed between the constraint members31, 32 is compressed by the load applied from the constraint members 31,32. A magnitude of the load is controlled by the electronic control unit300. The actuator 200 may be a hydraulic actuator. An example of a testdevice including the constraint members 31, 32 and the actuator 200includes Autograph®.

FIG. 6 is a diagram illustrating an example of the state of the battery100 while it is compressed. With reference to FIG. 6, when each of theconstraint members 31, 32 activated by the actuator 200 applies a loadto the battery 100, a flat part 20 a of the wound electrode body 20 iscompressed. Further, the winding core 40 is compressed by pressing theflat part 20 a of the wound electrode body 20 inward. Since the windingcore 40 contains an elastic material, the shape thereof is easilychanged. The shape of the winding core 40 is changed so as to extend inthe longitudinal direction by being pressed by the wound electrode body20. As such, a curved part 20 b of the wound electrode body 20 is alsocompressed.

Returning to FIG. 4, the electronic control unit 300 is configured todetermine whether a resistance increase due to distortion of anelectrode occurs in the battery 100. In more detail, when an electrode(for example, the positive electrode sheet 21 or the negative electrodesheet 22 illustrated in FIG. 3) composing the wound electrode body 20 ofthe battery 100 is distorted, a distance between the electrodes isincreased or a contact point (or a contact area) of the electrode activematerial is decreased, and electrical resistance of the battery 100tends to be increased due to a contact failure. The resistance increasein the battery 100 due to such distortion of the electrode istemporarily resolved by compressing the battery 100. In other words, theelectrode becomes close to its original form due to compression. Asdistortion of the electrode is decreased, electrical resistance of thebattery 100 is decreased. The electronic control unit 300 diagnoses thebattery 100, using such a phenomenon. In other words, the electroniccontrol unit 300 determines whether the resistance increase due todistortion of the electrode occurs in the battery 100 based on whetheran amount of decrease in electrical resistance of the battery 100 isless than a predetermined amount when the battery 100 is compressed.Details of a configuration of the electronic control unit 300 will bedescribed below.

As the electronic control unit 300, a microcomputer including aprocessor, a random access memory (RAM), and a storage device can beadopted. As the processor, for example, a central processing unit (CPU)can be adopted. The RAM functions as a working memory that temporarilystores data processed by the processor. The storage device is configuredto maintain information stored therein. The number of processorsincluded in the electronic control unit 300 is arbitrary, and may be oneor plural.

The electronic control unit 300 includes an information acquisition unit310, a first determination unit 320, and a second determination unit330. In the electronic control unit 300, the information acquisitionunit 310, the first determination unit 320, and the second determinationunit 330 are embodied by, for example, the processor and a programexecuted by the processor. However, the present disclosure is notlimited thereto, and each of these units may be embodied by dedicatedhardware (an electronic circuit).

The information acquisition unit 310 is configured to acquire a firstresistance value indicating a magnitude of electrical resistance of thebattery 100 before the compression, compress the battery 100, andacquire a second resistance value indicating a magnitude of electricalresistance of the battery 100 after the compression. In the presentembodiment, the information acquisition unit 310 is configured tocompress the battery 100 by controlling the actuator 200 such that theactuator 200 applies a load to the battery 100 from the outside (theconstraint members 31, 32). Hereinafter, the process in which theinformation acquisition unit 310 executes the compression is referred toas a “first compression process”.

Using the first resistance value and the second resistance valueacquired by the information acquisition unit 310, the firstdetermination unit 320 is configured to determine whether the amount ofdecrease in electrical resistance of the battery 100 by the firstcompression process is less than the predetermined amount. Hereinafter,the case where the amount of decrease in electrical resistance of thebattery 100 by the first compression process is less than thepredetermined amount is referred to as “resistance decrease exists”, anda case where the amount of decrease in electrical resistance of thebattery 100 by the first compression process is not less than thepredetermined amount is referred to as “no resistance decrease exists”.

Using the determination result of the first determination unit 320, thesecond determination unit 330 determines whether the resistance increasedue to distortion of the electrode occurs in the battery 100. Morespecifically, when the first determination unit 320 has determined that“resistance decrease exists”, the second determination unit 330recognizes that the resistance increase due to distortion of theelectrode occurs in the battery 100 (hereinafter, also referred to as“distortion exists”) and executes a predetermined process (hereinafter,also referred to as a “first diagnosis process”). On the other hand,when the first determination unit 320 has determined that “no resistancedecrease exists”, the second determination unit 330 recognizes that theresistance increase due to distortion of the electrode does not occur inthe battery 100 (hereinafter, also referred to as “no distortionexists”) and executes another predetermined process (hereinafter, alsoreferred to as a “second diagnosis process”).

In the present embodiment, the second determination unit 330 executes,as the first diagnosis process, a predetermined recovery process andrecording of a recovery history. FIG. 7 is a diagram for describing arecovery process executed by the second determination unit 330. Withreference to FIG. 7 together with FIG. 4, when an electrode of thebattery 100 is distorted and electrical resistance of the battery 100 isincreased, the second determination unit 330 executes the recoveryprocess. As such, distortion (and further, a contact failure) of theelectrode is resolved, and the battery 100 becomes close to a normalstate (that is, a state where no distortion occurs in the electrode).More specifically, the second determination unit 330 controls theactuator 200 such that the actuator 200 applies, to the battery 100, aload that compresses the battery 100. Hereinafter, the process in whichthe second determination unit 330 executes the compression (that is, aload is applied to the battery 100) is referred to as a “secondcompression process”. By controlling the charger/discharger 400, thesecond determination unit 330 charges the battery 100 in a dischargedstate in which the SOC thereof has become equal to or less than thepredetermined SOC value while a load is applied to the battery 100 bythe second compression process. Hereinafter, the process for chargingthe battery 100 while the battery 100 is compressed by the seconddetermination unit 330 is referred to as a “recovery process”. In thepresent embodiment, the load in the second compression process becomesgreater than the load in the first compression process. However, thepresent disclosure is not limited thereto, and the load in the firstcompression process may be the same as that in the second compressionprocess.

When the first determination unit 320 has determined that “resistancedecrease exists”, the recovery process is executed, such that distortionof the electrode in the battery 100 is resolved. More specifically, inthe present embodiment, carbon-based electrodes are adopted as thenegative electrodes of the battery 100 and ternary-based positiveelectrodes are adopted as the positive electrodes of the battery 100.Therefore, the negative electrodes are expanded during the charging ofthe battery 100 and contracted during the discharging of the battery100. The battery 100 according to the present embodiment is used, forexample, while being mounted on an electrically driven vehicle (that is,the charging and the discharging are repeated), and thus distortion(more specifically, deformation causing a gap between the electrodes) ofthe positive electrode easily occurs. In the recovery process,distortion of the positive electrode which has occurred due to the useof the battery 100 can be accurately resolved. In the recovery process,the battery 100 is charged. As the battery 100 is charged, the negativeelectrodes of the battery 100 are expanded. Then, as the negativeelectrodes are expanded, the positive electrodes are compressed. As thebattery 100 is charged while the battery 100 is compressed by the secondcompression process, the positive electrodes are tightly compressed andthe distorted positive electrode easily returns to its original form. Asthe distorted positive electrode becomes close to its original form,contact resistance (and thus, electrical resistance of the battery 100)in the positive electrode is decreased.

On the other hand, when the first determination unit 320 has determinedthat “no resistance decrease exists”, the second determination unit 330executes the second diagnosis process. The second diagnosis process doesnot include the above-described recovery process. In the presentembodiment, the second determination unit 330 records the diagnosisresult (that is, no distortion exists) in the tag TG, as the seconddiagnosis process.

FIG. 8 is a flowchart illustrating a procedure of a diagnosis processexecuted by the electronic control unit 300. A series of processesillustrated in the flowchart is started when, for example, a userinstructs the electronic control unit 300 to start diagnosis in a statewhere the battery 100 is set in the diagnostic device 1. At the start ofthe process, a load (hereinafter, also referred to as a “constraintload”) applied to the battery 100 by each of the constraint members 31,32 is substantially zero. The battery 100 (that is, the secondarybattery to be diagnosed) set in the diagnostic device 1 may be a batterycollected from an electrically driven vehicle.

With reference to FIG. 8 together with FIG. 4, in step (hereinafter,simply represented by “S”) 11, the information acquisition unit 310acquires electrical resistance of the battery 100. The informationacquisition unit 310 can acquire electrical resistance of the battery100 using the voltage and the current during the discharging and thecharging of the battery 100. The information acquisition unit 310charges and discharges the battery 100 by controlling thecharger/discharger 400. Further, the information acquisition unit 310acquires the voltage and the current of the battery 100 from themonitoring unit 110. Electrical resistance of the battery 100 acquiredin S11 corresponds to an example of the “first resistance value”according to the present disclosure. Any parameter indicating themagnitude of electrical resistance of the battery 100 can be adopted asthe first resistance value, but in the present embodiment, a parameterrepresented by an equation, “R=(OCV−CCV)/I” is adopted. In the presentembodiment, the information acquisition unit 310 acquires electricalresistance (R) by dividing a value, obtained by subtracting aclosed-circuit voltage (CCV) from an open-circuit voltage (OCV), by acurrent (I).

In S12, the information acquisition unit 310 compresses the battery 100.S12 corresponds to an example of the “first compression process”according to the present disclosure. In other words, the informationacquisition unit 310 compresses the battery 100 by controlling theactuator 200 such that the actuator 200 applies a load to the battery100 from the outside (the constraint members 31, 32). The magnitude ofthe load in S12 can be arbitrarily set, and may be, for example, 3 kN orgreater and 10 kN or less. In the present embodiment, the magnitude ofthe load in S12 is set to be 10 kN.

In S13, the information acquisition unit 310 acquires electricalresistance of the battery 100 while being compressed in the process ofS12. Electrical resistance of the battery 100 acquired in S13corresponds to an example of the “second resistance value” according tothe present disclosure. The second resistance value is acquired in thesame manner as the first resistance value. In other words, theinformation acquisition unit 310 calculates electrical resistance of thebattery 100 according to the above-described equation, “R=(OCV−CCV)/I”.

In S14, the first determination unit 320 determines whether the decreaseamount of electrical resistance of the battery 100 by the firstcompression process (S12) is greater than a predetermined value. Morespecifically, when a value (hereinafter, also referred to as a“resistance decrease amount”) obtained by subtracting the secondresistance value (that is, electrical resistance of the battery 100acquired in S13) from the first resistance value (that is, electricalresistance of the battery 100 acquired in S11) exceeds a predeterminedthreshold (hereinafter, also referred to as a “Th1”), the firstdetermination unit 320 determines that a resistance decrease exists (YESin S14). On the other hand, when the resistance decrease amount (=firstresistance value−second resistance value) is equal to or lower than Th1,the first determination unit 320 determines that no resistance decreaseexists (NO in S14). Th1 can be arbitrarily set and may be set based onan initial electrical resistance (that is, electrical resistance of thebattery 100 in the initial state). In the present embodiment, Th1 is setto be 10% of the initial electrical resistance. In other words, when theinitial electrical resistance is 1Ω, Th1 is set to be 0.1Ω.

When the resistance increase due to distortion of the electrode occursin the battery 100, distortion of the electrode is decreased by thefirst compression process (S12) and thus electrical resistance of thebattery 100 is decreased. In other words, when the determination in S14is negative, it means that the resistance increase due to distortion ofthe electrode does not occur in the battery 100. On the other hand, whenthe determination in S14 is positive, it means that the resistanceincrease due to distortion of the electrode occurs in the battery 100.Based on the result (YES/NO) of the determination (S14) by the firstdetermination unit 320, the electronic control unit 300 according to thepresent embodiment can accurately determine whether the resistanceincrease due to distortion of the electrode occurs in the battery 100.

When the determination in S14 is negative, the second determination unit330 executes the above-described second diagnosis process in S16. Morespecifically, the second determination unit 330 records, in the tag TGof the battery 100, information indicating that the resistance increasedue to distortion of the electrode does not occur in the battery 100.

The second diagnosis process is not limited to the recording of thediagnosis result as above, and may be a notification of the diagnosisresult. The method of notification is arbitrary, and the user may benotified by a display (for example, a display of characters or images)on a display device, by sound (including voice) through a speaker, or byturning on a predetermined lamp (including blinking). In addition, thesecond diagnosis process may include a process for transmitting thediagnosis result to a mobile terminal (for example, a tablet terminal, asmartphone, a wearable device, or a service tool) carried by the user.

On the other hand, when the determination in S14 is positive (resistancedecrease exists), the second determination unit 330 executes theabove-described first diagnosis process (in the present embodiment, therecovery process and the recording of the recovery history) in S15. FIG.9 is a flowchart illustrating details of the first diagnosis process(that is, a process executed when a resistance increase due todistortion of the electrode occurs in the secondary battery) executed inS15 in FIG. 8.

With reference to FIG. 9 together with FIG. 4, in S21, the seconddetermination unit 330 compresses the battery 100. S21 corresponds to anexample of the “second compression process” according to the presentdisclosure. In other words, the second determination unit 330 compressesthe battery 100 by controlling the actuator 200 such that the actuator200 applies a load to the battery 100 from the outside (the constraintmembers 31, 32). In the present embodiment, the load in S21 is greaterthan the load in S12. The magnitude of the load in S21 can bearbitrarily set, and may be, for example, 15 kN or greater and 50 kN orless. In the present embodiment, the magnitude of the load in S21 is setto be 20 kN.

In S22, the second determination unit 330 repeats the discharging andthe charging of the battery 100 a predetermined number of times. Thedischarging and the charging in S22 are executed while the load isapplied to the battery 100 by the second compression process (S21). Thesecond determination unit 330 can discharge and charge the battery 100by controlling the charger/discharger 400. S22 corresponds to an exampleof the “recovery process” according to the present disclosure. Thenumber of times of the discharging and the charging in the recoveryprocess can be arbitrarily set, and may be one or more and 50 or less.In the present embodiment, the number of times appropriate for resolvingdistortion, which is obtained in advance by experiments or simulation,is set to be a predetermined number of times. By the discharging, theSOC of the battery 100 becomes a predetermined first SOC value, and bythe charging, the SOC of the battery 100 is changed from the first SOCvalue to a predetermined second SOC value. The first SOC value may be,for example, 0% or greater and 50% or less. The second SOC value isgreater than the first SOC value, and may be, for example, 60% orgreater and 100% or less. In the present embodiment, the first SOC valueis set to be 0% and the second SOC value is set to be 100%. In S22, thecharging is executed a predetermined number of times such that the SOCof the battery 100 is increased from 0% to 100%. A charging anddischarging rate can be arbitrarily set, and may be, for example, 1 C.

By executing the process of S22, distortion of the electrode (forexample, a positive electrode) of the battery 100 is resolved, andelectrical resistance of the battery 100 is decreased. Then, in S23, thesecond determination unit 330 records, in the tag TG of the battery 100,the information indicating the history of the recovery process (forexample, a date when the recovery process has been executed, a load inthe second compression process, a SOC range in the recovery process, thenumber of times of discharging and charging, and a charging anddischarging rate). By executing the process of S23, S15 in a mainprocess (processes of FIG. 8) ends. Thereafter, S15 ends and the seriesof processes of FIG. 8 ends.

As described above, by executing the processes of S11 to S14 in FIG. 8,the electronic control unit 300 can accurately determine whether theresistance increase due to distortion of the electrode occurs in thebattery 100. Moreover, with the electronic control unit 300, it ispossible to execute the recovery process (S15 in FIG. 8) on the battery100, as needed. Distortion of the electrode is resolved by the recoveryprocess. As such, a state where deterioration of performance of thebattery 100 is resolved (that is, the state where electrical resistanceof the battery 100 is decreased) is basically maintained even if thecompression is released.

In the above embodiment, in the first compression process (S12 in FIG.8), the information acquisition unit 310 controls the actuator 200 suchthat the actuator 200 applies a load to the battery 100 from theoutside. However, the present disclosure is not limited thereto, and theinformation acquisition unit 310 may be configured to compress thepositive electrodes of the battery 100 by expanding negative electrodesof the battery 100. More specifically, in the first compression process(S12 in FIG. 8), the information acquisition unit 310 may control thecharger/discharger 400 such that the SOC of the battery 100 is increaseduntil the negative electrodes are expanded while the battery 100 ispressed by the constraint members 31, 32 (that is, a state where thethickness of the battery 100 is constant), thereby compressing thepositive electrodes. With such a method, the positive electrodes of thebattery 100 can be easily compressed in the first compression process.Alternatively, the negative electrodes of the battery 100 may beexpanded by changing the temperature. For example, in the firstcompression process (S12 in FIG. 8), the temperature of the battery 100may be increased until the negative electrodes of the battery 100 areexpanded while the battery 100 is pressed by the constraint members 31,32.

In S15 in FIG. 8, a process illustrated in FIG. 10 may be executedinstead of the process illustrated in FIG. 9. FIG. 10 is a flowchartillustrating a modified example of the process illustrated in FIG. 9.The process of FIG. 10 is the same as that of FIG. 9 except that S22Aand S22B are adopted instead of S22 (see FIG. 9). Hereinafter, S22A andS22B will be described.

With reference to FIG. 10 together with FIG. 4, in S22A, the seconddetermination unit 330 discharges the battery 100 such that the SOCthereof becomes the first SOC value (for example, 0%) and charges thebattery 100 such that the SOC thereof is increased from the first SOCvalue to the second SOC (for example, 100%). Then, in S22B, the seconddetermination unit 330 determines whether electrical resistance of thebattery 100 is equal to or lower than a predetermined threshold(hereinafter, also referred to as “Th2”). Th2 can be arbitrarily set,and may be set based on electrical resistance of the battery 100 in theinitial state. The processes of S22A and S22B are executed while theload is applied to the battery 100 by the second compression process(S21). When the determination in S22B is negative, the processes of S22Aand S22B are repeated. Electrical resistance of the battery 100 tends tobe decreased every time the process of S22A is executed. On the otherhand, when the determination in S22B is positive (that is, electricalresistance is equal to or lower than Th2), the process proceeds to S23.When the determination in S22B is still negative even if the processesof S22A and S22B are executed more than a predetermined number of times,the process of FIG. 10 may be stopped due to a timeout.

According to the process illustrated in FIG. 10, while the load thatcompresses the battery 100 is applied to the battery 100, thedischarging of the battery 100, which makes the SOC thereof become equalto or less than a predetermined SOC value, and the charging of thebattery 100 in a discharged state in which the SOC thereof has becomeequal to or less than the predetermined SOC value are repeated untilelectrical resistance of the battery 100 becomes a value equal to orless than a predetermined value. As such, by repeating the dischargingand the charging, electrical resistance of the battery 100 issufficiently and easily decreased. In S22B, electrical resistance of thebattery 100 may be measured while the compression by the secondcompression process (S21) is temporarily released and the battery 100 isnot compressed.

In the above embodiment and the modified example, in S15 in FIG. 8, thebattery 100 is discharged and charged while the load that compresses thebattery 100 is applied to the battery 100. In order to verify the effectof such a recovery process, the inventors of the present disclosureprepared a positive electrode “NCM”, a negative electrode “carbon”, aseparator “PP/PE/PP”, and a winding-type lithium-ion secondary batteryhaving a capacity of 25 Ah, and caused a resistance increase due todistortion of the electrode to occur in the lithium-ion secondarybattery. As such, the capacity of the lithium-ion secondary battery wasdecreased by 30% of the initial state, and electrical resistance thereofwas increased by 60% of the initial state. Then, a recovery process wasexecuted on such a lithium-ion secondary battery under the followingconditions.

Temperature: approximately 25° C.,

compression load: 20 kN,

SOC range: 0% to 100%,

charging and discharging rate: 1 C,

time during which the recovery process is executed: 1 hour

By executing the recovery process, the lithium-ion secondary batteryrecovered to a state where the capacity thereof is decreased by 20% ofthe initial state and electrical resistance thereof is decreased by 40%of the initial state. In other words, by executing the recovery process,distortion of the electrode could be resolved and the resistanceincrease due to distortion of the electrode could be restricted.Further, for comparison, instead of the recovery process, a process ofleaving the battery 100 at 60° C. for 40 hours was executed. However,such a high-temperature process did not resolve the resistance increasedue to distortion of the electrode.

The first diagnosis process does not have to include the recoveryprocess. When the first determination unit 320 has determined that“resistance decrease exists”, the second determination unit 330 may onlyrecord the diagnosis result as the first diagnosis process. In otherwords, when the diagnosis has ended, the second determination unit 330may be configured to record the diagnosis result (distortion exists/nodistortion exists) in the tag TG. Moreover, when the diagnosis hasended, the second determination unit 330 may be configured to notify auser of the diagnosis result in addition to or instead of recording thediagnosis result.

The battery 100 diagnosed and/or resolved by the process of FIG. 8 maybe mounted on an electrically driven vehicle. The battery 100 may bemounted on an electrically driven vehicle while the load is applied tothe battery 100 (that is, the battery 100 is constrained). The magnitudeof the load applied to the battery 100 in the electrically drivenvehicle may be determined based on the history of the recovery processstored in the tag TG of the battery 100.

An assembled battery may be manufactured using a plurality of batteries100 diagnosed and/or resolved by the process of FIG. 8. Secondarybatteries used for manufacturing the assembled battery may be selectedbased on the history of the recovery process stored in the tag TG. Theassembled battery may be manufactured by collecting secondary batterieshaving similar magnitude of applied loads indicated in the history ofthe recovery process stored in the tag TG, and mounted on theelectrically driven vehicle. FIG. 11 is a diagram illustrating anexample of an assembled battery.

With reference to FIG. 11, an assembled battery 600 includes a pluralityof batteries 100 and a plurality of spacers 610 which are alternatelyarranged. The spacers 610 are formed of, for example, a resin platematerial. However, the shape and material of the spacer 610 are notlimited thereto, and can be appropriately changed. Each of the batteries100 may be, for example, a lithium-ion secondary battery on which therecovery process (S15 in FIG. 8) has been executed with the applied loadhaving the magnitude similar to each other. Each of the batteries 100includes a positive electrode terminal 51, a negative electrode terminal52, and a gas discharge valve 53. The batteries 100 are electricallyconnected to one another in series. In more detail, each of thebatteries 100 that compose the assembled battery 600 is arranged withtheir direction reversed one by one. Then, the positive electrodeterminal 51 of one of the batteries 100 and the negative electrodeterminal 52 of another adjacent one are electrically connected by aconnecting member 620 (for example, a bus bar). Constraint plates 631,632 are respectively arranged at both ends of the assembled battery 600in the arranging direction D. Moreover, the constraint plate 631 and theconstraint plate 632 are connected to each other via a constraint band641. The constraint band 641 and the constraint plates 631, 632 areconnected by screws 642. By tightening the screw 642, each of thebatteries 100 can be compressed. Using the screws 642, the pressure (aconstraint force) applied to the batteries 100 and the spacers 610 canbe adjusted. The constraint force may be determined based on the historyof the recovery process stored in the tag TG (see FIG. 4) of eachbattery 100.

In the above embodiment, the winding core 40 (see FIG. 6) contains anelastic material. However, the winding core 40 does not have to containthe elastic material. By forming the winding core 40 with a hardmaterial, the flat part 20 a is easily and tightly compressed.

In the above embodiment, carbon-based electrodes are adopted as thenegative electrodes of the lithium-ion secondary battery. However, amaterial of the negative electrodes is not limited thereto, and can beappropriately changed. For example, the negative electrodes of thelithium-ion secondary battery may be silicon-based electrodes. Insteadof a carbon-based material, a silicon-based material (for example,silicon, silicon alloy, or SiO) may be adopted. Further, a material ofthe positive electrodes can also be appropriately changed.

The secondary battery to be diagnosed is not limited to the liquidlithium-ion secondary battery, and may be another type of liquidsecondary battery (for example, a nickel hydrogen secondary battery) oran all-solid-state secondary battery. The secondary battery to bediagnosed may be a multilayer flat plate type (stack type) secondarybattery instead of the winding-type secondary battery. The secondarybattery to be diagnosed is not limited to the secondary battery forvehicles, and may be a stationary secondary battery.

The embodiment disclosed herein needs to be considered as illustrativein all points and not restrictive. The scope of the present disclosureis shown not by the above description of the embodiments but by theclaims, and is intended to include meanings equivalent to the claims andall modifications within the scope thereof

What is claimed is:
 1. A diagnostic device for a secondary batteryhaving a structure in which positive electrodes and negative electrodesare alternately arranged, the diagnostic device comprising: anelectronic control unit configured to: acquire a first resistance valueindicating a magnitude of electrical resistance of the secondary batterybefore compression, and compress at least a part of the secondarybattery; acquire a second resistance value indicating a magnitude ofelectrical resistance of the secondary battery after the compression;determine, using the first resistance value and the second resistancevalue, whether an amount of decrease in electrical resistance of thesecondary battery by the compression is greater than a predeterminedvalue; and determine whether an increase in electrical resistance due todistortion of at least one of the positive electrodes and the negativeelectrodes occurs in the secondary battery using a result of thedetermination on the amount of decrease in electrical resistance.
 2. Thediagnostic device according to claim 1, wherein: the electronic controlunit is configured to, upon determining that the increase in electricalresistance due to the distortion of at least one of the positiveelectrodes and the negative electrodes occurs in the secondary battery,execute a predetermined recovery process; and the predetermined recoveryprocess includes charging, while a load that compresses the secondarybattery is applied to the secondary battery, the secondary battery in adischarged state in which a state-of-charge (SOC) of the secondarybattery has become equal to or less than a predetermined SOC value. 3.The diagnostic device according to claim 2, wherein the predeterminedrecovery process includes repeating, while the load that compresses thesecondary battery is applied to the secondary battery, discharging thesecondary battery such that the SOC of the secondary battery becomesequal to or less than the predetermined SOC value and charging thesecondary battery in the discharged state in which the SOC of thesecondary battery has become equal to or less than the predetermined SOCvalue, until electrical resistance of the secondary battery becomesequal to or less than a predetermined value.
 4. The diagnostic deviceaccording to claim 1, wherein the electronic control unit is configuredto compress the secondary battery by applying a load from an outside ofthe secondary battery.
 5. The diagnostic device according to claim 1,wherein the electronic control unit is configured to compress thepositive electrodes of the secondary battery by expanding the negativeelectrodes of the secondary battery.
 6. A recovery method for asecondary battery having a structure in which positive electrodes andnegative electrodes are laminated, the recovery method comprising: afirst compression for compressing at least a part of the secondarybattery; a second compression for compressing the secondary battery byapplying a load from an outside of the secondary battery when an amountof decrease in electrical resistance of the secondary battery by thefirst compression is greater than a predetermined value; and a recoveryfor charging the secondary battery in a discharged state in which astate-of-charge (SOC) of the secondary battery has become equal to orless than a predetermined SOC value while the secondary battery iscompressed by the second compression.
 7. The recovery method accordingto claim 6, wherein: the secondary battery is a lithium-ion secondarybattery; and the negative electrodes of the secondary battery arecarbon-based electrodes or silicon-based electrodes.
 8. The recoverymethod according to claim 7, wherein, in the first compression, thepositive electrodes are compressed by increasing the SOC of thesecondary battery until the negative electrodes are expanded.
 9. Therecovery method according to claim 6, wherein: the secondary batteryincludes a wound electrode body that includes the positive electrodesand the negative electrodes; the positive electrodes and the negativeelectrodes are wound around a winding core while being alternatelyarranged with separators interposed between the positive electrodes andthe negative electrodes; a longitudinal direction of the winding core isperpendicular to a winding axis of the wound electrode body; and thewinding core contains an elastic material and is configured to extend inthe longitudinal direction by a pressing force received from the woundelectrode body.